1. Field of the Invention
This invention relates to a method of making a Selective Absorber which is applied to a glass substrate. The Selective Absorber has a high absorption coefficient for solar energy incident on the absorber, often referred to as solar absorptance, and a low emission coefficient for infrared radiation which corresponds to the operating temperature of the absorber, often referred to as infrared emittance. The Improved Selective Absorber disclosed herein would have particular application in the field of solar energy collecting systems of the type having an outer glass housing which holds a vacuum and an inner glass tube for transporting a heatable fluid therethrough. The Selective Absorber being suited for application to the outer surface of the inner tube.
2. Description of the Prior Art
A number of selective absorbing surfaces have been developed which offer a variety of coefficients of absorptance and coefficients of emittance over a wide spectrum of incident radiation. Even though a number of selective absorbing surfaces have been developed, Selective Absorbers applied to glass have generally been expensive and limited in tube length since these have been obtained principally by vacuum deposition. Prior to the method of this invention an inexpensive Selective Absorber on a glass substrate of arbitrary length was simply not available.